1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper feeding device which helps prevent double feeding of a sheet of paper and improves the paper feeding capability, and an image forming apparatus having the same.
2. Description of the Related Art
In general, a paper feeding device which picks up a sheet of paper stacked in a paper feeding cassette and feeds a picked-up sheet of paper to a printing unit installed inside of an image forming apparatus, is provided in an image forming apparatus such as a printer or a copying machine. An example of a conventional paper feeding device is shown in FIG. 1.
Referring to FIG. 1, the conventional paper feeding device includes a paper feeding cassette 71 on which a sheet of paper is stacked, a pickup roller 72 which picks up the sheet of paper from the paper feeding cassette 71, and a double feeding prevention member 73 which prevents double feeding of a sheet of paper.
The paper feeding cassette 71 includes a knock-up plate 71a on which a sheet of paper is stacked, and an elastic member (not shown), which elastically biases the knock-up plate 71a in an upward direction. The sheets of paper stacked on the knock-up plate 71a are fed by the pickup roller 72 one by one. A friction member 10 is disposed on an upper surface of the knock-up plate 71a which faces the pickup roller 72, so as to prevent double feeding of a sheet of paper. The friction member 10 provides a surface that creates greater frictional force than the frictional force between a sheet of paper and the rear surface of a last sheet of paper, thereby preventing double feeding of a sheet of paper.
The double feeding prevention member 73 includes a friction pad 4, which is disposed below the pickup roller 72, and prevents double feeding of a sheet of paper fed by the pickup roller 72. The friction pad 4 is attached to one side of the double feeding prevention member 73. The friction pad 4 provides a friction resistance to the rear surface of the sheet of paper fed by the pickup roller 72. In other words, even though a plurality of sheets of paper are fed by the pickup roller 72, progression of other sheets of paper is suppressed, and only the sheet of paper stacked on the knock-up plate 71a is fed.
An entrance portion 70 which is positioned between the pickup roller 72 and the friction pad 4 to prevent double feeding of sheets of paper, is formed with an opening size of 1-1.5 mm. A curl is produced on a front end of the sheet of paper fed by the pickup roller 72 from the entrance portion 70. When the size of the entrance portion 70 is large, the front end of the sheet of paper on which the curl is produced easily enters into the entrance portion 70, and the frequency of double feeding of a sheet of paper increases. Conversely, when the size of the entrance portion 70 is small, the frequency of double feeding of a sheet of paper decreases but the frequency of paper jams caused when the front end of the sheet of paper becomes jammed on the double feeding prevention member 73 increases due to the increased friction between the fed sheet of paper and the double feeding prevention member 73. As a result, paper feeding performance is degraded.
As described above, in the prior art, when the dimensions of the entrance portion 70 are minimized, the frequency of double feeding of a sheet of paper decreases, but the frequency in which the sheet of paper is jammed on the double feeding prevention member 73 increases according to the shape of the curve of the front end of the sheet of paper. In addition, when the dimensions of the entrance portion 70 are minimized, the friction between the lower side of the fed sheet of paper and the double feeding prevention member 73 increases, which reduces the paper feeding force. But when the paper feeding force of the sheet of paper generated by the pickup roller 72 increases, the surface of the pickup roller 72 wears more quickly than normal.